The entire text of each of the following disclosures is specifically incorporated herein by reference without disclaimer: Ser. No. 07/945,865, filed Sep. 16, 1992; Ser. No. 07/800,832, filed Dec. 2, 1991; Ser. No. 07/410,727, filed Sep. 20, 1989, now issued as U.S. Pat. No. 5,128,319; and Ser. No. 07/090,646 filed 28 Aug. 1987.
1. Field of the Invention
The present invention relates generally to compositions and methods for binding to and inactivating viruses and for protecting cells from viral infection. More particularly, it concerns compositions and methods for binding to and inactivating HIV gp120 and protecting target CD4.sup.+ cells, such as T cells, from infection by HIV. Peptides including short CD4 receptor sequences are identified which are surprisingly effective at interacting with HIV gp120 and in inhibiting or reducing HIV infection of human CD4.sup.+ cells. The invention thus encompasses improved CD4-based peptide formulations with gp120 binding functions and HIV-infection inhibitory activity.
2. Description of the Related Art
AIDS was first recognized in the United States in 1981; the number of cases has been increasing at a dramatic pace since then. Several million AIDS infections have now been reported in the United States alone (Rees, 1987). Once significant immunosuppressive symptoms appear in an infected individual, the expected outcome of the infection is death. There is currently no known treatment that can indefinitely delay or prevent the fatal consequences of the disease. Although the disease first manifested itself in homosexual or bisexual males and intravenous drug abusers, it has now spread to others by means such as intimate sexual contact with or receipt of blood products from a carrier of the virus.
The causative agent associated with AIDS has been identified as a group of closely related retroviruses commonly known as Human T Cell Lymphotrophic Virus-type III (HTLV-III), Lymphadenopathy Viruses (LAV), AIDS-Related Viruses (ARV), or more recently named Human Immunodeficiency Virus (HIV). These viruses will be collectively referred to herein for convenience as HIV.
Like other retroviruses, HIV has RNA as its genetic material. When the virus enters the host cell, a viral enzyme known as reverse transcriptase copies the viral RNA into a double stranded DNA. The viral DNA migrates to the nucleus of the cell where it serves as a template for additional copies of viral RNA which can then be assembled into new viral particles. The viral RNA can also serve as messenger RNA (mRNA) for certain viral proteins, including the viral core proteins p18, p24 p13, and reverse transcriptase. RNA may also or be "spliced" into specific viral mRNAs necessary to produce several other viral proteins including two glycosylated structural proteins known as gp41 and gp120 which are inserted in the outer membrane of the virus (Wain-Hobson et al., 1985). Purified gp120 is known to induce antibody in the goat, horse and rhesus monkey that neutralizes HIV in lab tests (Robey et al., 1986).
The primary event in the infection of target cells by HIV is the interaction between the external viral envelope glycoprotein, gp120, and its cellular receptor, CD4 (Lasky et al., 1987). Although the gp120:CD4 interaction is essential for HIV-1 entry into cells, this knowledge has yet to lead to the development of an effective clinical strategy to prevent HIV infection. Certain peptides from gp120 V3 function to inhibit HIV infection (U.S. patent application Ser. No. 07/945,865). However, De Rossi et al. (1991) reported that V3-derived synthetic peptides actually enhanced HIV-1 infection of cells through a CD4-dependent mechanism.
The CD4 molecule has been investigated as a basis for developing anti-HIV strategies. CD4 constructs have been designed with the aim of killing cells already infected with HIV. Such conjugates include CD4 molecules linked to Pseudomonas exotoxin, or Ricin A Chain, which have been reported to selectively kill HIV-infected cells (Chaudhary et al., 1988; Till et al., 1988). CD4 peptide-toxin conjugates have also been shown to be effective at killing HIV-infected cells (PCT Patent Application, WO 91/04050).
The properties of CD4 and CD4-based constructs have also been investigated in regard to inhibiting HIV infectivity. For example, recombinant soluble CD4 molecules (rsCD4) have been shown to neutralize and inhibit AIDS virus infection in vitro (Deen et al., 1988; Traunecker et al., 1988), and to have some beneficial effects in rhesus monkeys infected with simian immunodeficiency virus of macaques (Watanabe et al., 1989). Certain CD4 conjugates have also been constructed, including CD4 "immunoadhesins" in which a CD4 segment is linked to an antibody Fc portion (Capon et al., 1989), and CD4 segments conjugated to ovalbumin (Ghetie et al., 1991). However, such molecules, being relatively large, have many drawbacks which limit any potential therapeutic usefulness.
Smaller molecules, including CPFs (Findberg et al., 1990) and certain CD4-based peptides (Jameson et al., 1988; Arthos et al., 1989), have also been assessed as potential anti-HIV agents. However, this has not lead to the identification of any particularly effective inhibitory compounds. Other non-peptide therapeutic agents, particularly AZT, have recently shown disappointing results in longer-term clinical trials in AIDS patients (Cohen et al., 1993). It is therefore evident that there is currently a great need for improved anti-HIV agents, particularly those capable of inhibiting HIV infection of target cells.